1. Field of the Invention
The present invention relates to an information retrieval apparatus for automatically retrieving desired information in a recording medium such as a film by detecting a mark on the information recording medium, suitable for use in a microfilm reader or film reader/printer.
2. Related Background Art
In a conventional retrieval apparatus used in a film reader, a retrieval mark put on a side of each frame of a film is optically detected and counted so that a desired frame in the film is automatically retrieved.
In such a retrieval apparatus, the marks on the film are illuminated by a lamp, a change of light interrupted by the marks when the film is driven is detected by a mark sensor, an output signal of the mark sensor is counted by a counter, the count of the counter is compared with a frame number of a desired frame entered by a keyboard by a comparator, and when they are equal, a stop signal is generated by the comparator to a drive control circuit to stop a drive system which drives the film so that the desired frame is stopped at a predetermined projection position on a screen.
The film used in a projection device such as film reader or film reader printer may be a film 2 having a line of recorded images 1 as shown in FIG. 6 or a film 4 having two lines of recorded images 3 as shown in FIG. 7, where m denotes a retrieval mark put on a side of each image. The film 4 is called a duo film which is prepared by photographing images on one side of the film sequentially from a leading end of the film, and when one side has been photographed, reverse-loading the film and photographing images on the remaining side of the film sequentially from a trailing end of the film. It is thus prepared in a reciprocal photographing manner. In FIG. 6, the left side in the leading end of the film and the right side is the trailing end of the film. The images in the film 4 have been photographed in the sequence of numbers put on the images (which are actually not recorded but shown for a sake of convenience of explanation). A retrieval mark m is recorded on a side of the film for each image frame in order to allow retrieval of the image. In the duo film, an interval of the retrieval marks is small because a photographing reduction ratio is large while the interval of marks in the conventional film shown in FIG. 6 is relatively large.
In the prior art, when an address B is to be retrived starting from a current address A as shown in FIG. 12, the film is first moved at a high speed, the speed is reduced to a medium speed b frames before the desired address, the speed is further reduced to a low speed a frames before the desired address, and the film is stopped at the desired address B. The number of frames at which the speed is to be changed is determined by a braking performance of a film drive unit. There are various mark intervals of the film as described above. In the prior art, the stop sequence for the film is determined in accordance with a shortest mark interval so that the desired frame does not run over the predetermined stop position. As a result, if a film having a long mark interval is used, the speed is changed for before the desired frame and hence a retrieval time required to position the desired frame at the predetermined position is long.
In the prior art, an upper limit of the film drive velocity in the information retrieval apparatus is determined by a speed to detect and process the retrieval marks. If the film drive speed is determined based on the duo film having a small mark interval and the information is retrieved from a film having a long retrieval mark interval as shown in FIG. 2, the retrieval speed is low because the film is driven at the speed designed for the duo film in spite of the fact that a faster drive speed may be used.